Comparative analysis of the consumption of energy of two wood pulping processes

Equations are presented for the cumulative energy analysis of a process with numerous recycle streams and multiple products. The equations enable a quantitative assessment for alternative processes in the production of a particular product. This method was applied to the production of chemical pulp from wood by the Kraft process and a proposed alcohol extraction process. The Kraft process was found to be superior to the alcohol extraction process in terms of specific cumulative energy consumption for the production of chemical pulp (50% consistency) as the only useful product: 14.5 vs. 19.9 MJ/kg. However, if by products of the alcohol extraction process are considered as useful products, the specific cumulative energy consumption of the chemical pulp is reduced to 12.3 MJ/kg, which is below that of the Kraft process. Cogeneration of steam and electricity decreases the specific energy consumption for pulp production significantly for both processes. Various cogeneration strategies will be presented for the two processes. (C) 2000 Elsevier Science Ltd. All rights reserved.